1. Field
One embodiment of the invention relates to a private branch exchange (hereinafter referred to as PBX) and a telephone switching system.
2. Description of the Related Art
Conventionally, a PBX capable of displaying caller ID information such as a caller telephone number onto a display of a private telephone set housed in the PBX has been proposed.
It is disclosed by, for example, Japanese Patent Application Publication KOKAI No. H10-174134.
This PBX receives caller ID information indicating a caller telephone number on a public switched telephone network (PSTN) side to a PBX on an incoming call side, then, displays the caller ID information onto a display of the PBX on the incoming call side.
In caller ID information is usually communicated in a packet form in which the caller ID information is divided into some items thereof and can be included a caller name, a calling date and time, a caller telephone number non notice reason, caller telephone number expansion information, etc., other than the caller telephone number.
Such a PBX to treat the caller ID information generally determines whether or not it has received whole items of the caller ID information from a PSTN depending on the fact whether or not a specified time has already elapsed from a start of a reception of the caller ID information. That is, the PBX transmits the caller ID information to a telephone set on the incoming call side after a specified time from a reception of a packet of the first caller ID information. However, as mentioned above, since it is possible for the caller ID information to include a variety of items of information other than the caller telephone number, a data quantity becomes large sometime. Therefore, the PBX has to set the specified time being a threshold longer and the transmission of the caller ID information to the telephone set on the incoming call side delays even when the caller ID information is small in quantity. In contrast, if the threshold is set smaller, the caller ID information having a large data quantity cannot be received up to its end.